None of the existing models of the respiratory control system adequately explain the precise relationship between the increase of ventilation and that of metabolism; nor do they explain the patterns of ventilation at the onset or offset of exercise. The proposed studies are based on the hypothesis that neural input to the respiratory control system and neural mechanisms within the system are more important than traditionally believed. The studies use the neural output of the respiratory control system to represent ventilation, thereby allowing the use of "open loop" experimental conditions which avoid the negative chemical feedback associated with changes in ventilation. The first step has been to develop methods of handling phrenic nerve and respiratory muscle activity so that an objective and repeatable neural equivalent of tidal volume, a neural representation of central respiratory drive, is obtained. These activities are used in paralyzed ventilated animals, i.e., with chemical feedback loop opened, to study the input-output characteristics of the respiratory control system in response to neural stimuli. Specifically, it is proposed to extend studies on the ability of the control system to maintain its output as a result of feedback - stimulation or self-smplification in the medulla and pons. Further studies of the anatomical location of the mechanism will be carried out, and the possibility that it is the source of tonic excitation of the respiratory control system will be explored. The findings should lead to a better understanding of control mechanisms during both resting and exertional breathing.